High IQ / Dysfunction link.

The tortured genius is more than just a literary trope. There does seem to be a link between very high IQ and some sort of mental/social issues. If the article above is to be trusted, at the higher ranges maladjustment is extremely common, afflicting about half of the population under study. It seems to hold true to a lesser degree at the lower ranges of high IQ, with the problem becoming unignorable at the "visionary" 150+ range. I think this can be explained to some degree by modern sensory and information overload, and the misanthropy that is to be expected in dealings with more extroverted, superficial and unintelligent folk. However, for it to exist to this degree, there must be something inherent in high IQ that leads to such destabilization. So how does that affect the sub-120 IQ cull thought experiment? Would, in that vision, a depopulated but not necessarily IQ stratified humanity be the logical end result? Would it be better to reduce the population in every IQ category in proportion, culling entirely the absolute end of the spectrum but keeping alive a large proledom that would be ruled over by high IQ elites? A casted society perhaps, like ancient India, even if the castes are not exactly prescribed.

I think such a future awaits America, with the creation of a large lower block of hispanics and blacks and a high IQ minority of whites (by that time depopulated), very rare jews, mostly East Asians and a smattering of South Asians (of certain subethnies, as Indian origin people have always intermarried within castes even when they have been abolished). Such a population makeup, plus democracy, spells disaster. However, with a different system of government that does not rely on majority opinion, I think this population makeup can work as long as everyone is on the same ideological page. Unlikely though that is, I don't think it is impossible.

Well, it's pretty self-evident that a degree of intelligence far beyond the norm will isolate you socially. I guess the distinction between dysfunction and social awkwardness/remoteness then comes into play. I'm not sure it would be a major issue in a society which didn't aim to replace all meaningful human relations with trivial socialization. At least, such high IQ types would be regarded as strange, but encouraged to use their IQ towards greatness (the great composers, philosophers, etc spring to mind). If they were in the "extremely high" range, you would hope your eugenics was good enough to produce enough similar individuals to prevent total isolation. However, since it isn't an exact science, uber-intelligent "freak" types (150+) could always occur, and they would most likely be completely isolated, "unstable" of you will. So be it.

I'm not sure why you think it's possible that different ethnic groups would be able to build/maintain a lasting civilization. I'm not sure that a ruling class of high IQ individuals would be able to prevent the type of problems we know are inherent to multiculturalism. The absence of democracy in this scenario would simply remove political power from the lower strata; however, revolutions and the like are still possible without it. Of course, if everyone is on the same ideological page, no worries. We know that this is never the case, and ideology varies between class, caste, ethnic group, religious affiliation etc, quite fundamentally.

I appreciate that the scenario seems unlikely on its face. I envisioned something slightly derived from the Ottoman millat system (explained here). It would be fragile, but if each population accumulates in certain discrete geographical regions, it does not seem to me to be entirely implausible. There already seems to be movement towards a white dominant area in the form of the Pioneer Little Europe movement; which I think we will see a lot more of as the white population recedes due to low fertility.

Don't get me wrong, I don't think this will be lasting or even that this is satisfactory. I only say that it could be functional which is the best that can be hoped for if current trends continue. The preference would always be for ethnic homogeneity. It is not an ideal situation by any means, just conjecture towards a possible future. As for how the majority will end up on the same ideological page, I think some major disaster could provide the impetus for this. In an age where disaster seems right around the corner, this appeals as a possible scenario.

The herding together of similar high IQ individuals to reduce this tendency provides, I think, only part of an answer. If it is an inherent problem, this is not a solution, just something you expect these people to do. Gender dysphoria also seems to be very prevalent amongst high-IQ types, as well as openness (and I believe, a tendency towards liberalism).

I agree that the scenario could occur, and that current trends show something similar to what you're describing may happen, especially in a country like America (is there any other?).

But as you pointed out, it is not ideal. Interesting link to the Ottoman sub-system. Similar systems were in place in many Islamic caliphates of the past. I think why those had some semblance of stability was because the minority (or in the case of the Ottaman millat, non-Turkic) groups were small (mostly), and more importantly, far removed from the effects of the ruling class. In other words, in the absence of globalization, autonomy while being part of a larger societal structure was real autonomy, and not just freedom to trade, drink, and be merry, which is basically the autonomy sovereign states experience today.